1. Field of the Invention
This invention relates generally to a control system for an aircraft using acceleration feedback data to compensate for destabilizing forces exerted on the aircraft. More particularly, this invention relates to an aircraft model-following control system using acceleration feedback data that is combined with a command input to generate an error signal to compensate for destabilizing forces exerted on the aircraft. This feedback system results in reduced oscillational effects on the aircraft.
2. Brief Description of the Art
Aircraft, such as helicopters and fixed wing airplanes are subject to forces in the X (roll), Y (pitch) and Z (yaw) rotational directions. Destabilizing roll, pitch and yaw forces influence the flight path of the aircraft. These forces, also referred to as oscillations, can be external forces such as wind gusts, or internal forces, such as rotor aeroelastic resonance, or a combination of internal and external forces. The destabilizing forces present ride comfort problems and adversely affect aiming accuracy during targeting tasks. Regardless of the source of the destabilizing forces, in order to maintain a stable flight path, it is necessary to compensate for these forces.
Various conventional helicopters and fixed wing airplanes generally have only a primary flight control system (PCFS). In an aircraft with only PFCS, the operator of the aircraft must manually adjust the command stick in the control section of the aircraft to actuate a compensation force to offset the destabilization forces exerted on the aircraft. In an aircraft such as a helicopter, the operator must move the command stick to actuate a swashplate that will alter the pitch of the rotor blades in an attempt to compensate for destabilization forces experienced by the helicopter. These primary flight control systems (PFCS) do not include active feedback mechanisms to dynamically adjust or compensate for roll, pitch, and yaw forces exerted on the aircraft.
More progressive aircraft have an automatic flight control system (AFCS) in addition to the PFCS. The AFCS includes feedback mechanisms to compensate for undesired destabilization forces acting on the aircraft. The conventional AFCS utilize rate and attitude feedback to programmably adjust for destabilization forces exerted on the aircraft. Unfortunately, the rate and attitude vectors received from sensors on the aircraft do not always adequately adjust for the destabilization forces acting on the aircraft. This poor response to destabilization forces prohibits the aircraft from maintaining the desired stable flight path.
Some current production helicopters feature a hingeless or bearingless main rotor (BMR) design, which rely on aeromechanical control of the rotor and typically stabilize aircraft oscillations using conventional digital flight control solutions. Unfortunately, the BMR design inherently generates blade lead-lag oscillations that can significantly degrade flight path stability. The use of elastomeric flexing to dampen blade lead-lag motion is limited by the relatively small amplitude of blade motion.
Several references disclose vibration-reducing systems and are discussed as follows:
U.S. Pat. No. 4,819,182 entitled, "Method and Apparatus for Reducing Vibration of a Helicopter Fuselage", issued to Stephen P. King et al. discloses a method of reducing vibration of a helicopter fuselage using actuators and accelerometers. This reference does not disclose using an input from the operator, or any intelligence from a model.
U.S. Pat. No. 4,989,466 entitled, "Gyroscopically Stabilized Sensor Positioning System", issued to Ronald C. Goodman discloses a stabilized platform for mounting a camera or other sensor that is suspended from a support post. A universal joint is powered by a torque motor. A gyro stabilizer comprising three orthogonally arranged gyroscopes is mounted on the platform. Position sensors detect the angles of the three gyroscopes and provide inputs to servo control loops. This reference does not disclose using pilot input as a component of the stabilizing force nor does it disclose combining pilot input with acceleration feedback.
U.S. Pat. No. 5,124,938 entitled "Gyroless Platform Stabilization Techniques", issued to Marcelo C. Algrain, discloses an apparatus for platform stabilization. The apparatus uses linear and/or angular accelerometers to derive the roll, pitch and yaw components of the angular velocity of the vehicle the apparatus is mounted on. A control system implements a velocity control system or an acceleration control system. This reference does not disclose combining the output of the accelerometers with pilot command signals to reduce the effects of rotor oscillations.
U.S. Pat. No. 5,222,691 entitled "Automatic Turn Coordination Trim Control for Rotary Wing Aircraft", issued to Philip J. Gold et al., discloses a helicopter flight control system that uses an automatic turn coordination system that provides a coordinating yaw command signal to the tail rotor of the helicopter. The system stores on command signals indicative of bank angle, lateral ground speed and lateral acceleration thereby providing the pilot with automatic turn coordination about attitudes other than wings level. This reference does not disclose using acceleration vector data as feedback to reduce vibrations in the aircraft.
U.S. Pat. No. 5,634,794 entitled "Aircraft Simulator and Method", issued to Bruce L. Hildreth et al., discloses an apparatus and method for simulating a desired response in accordance with an external applied force. The apparatus includes a member that is responsive to the applied force, an actuator coupled to the member, and a force sensor for detecting the applied force. This reference does not disclose using acceleration vector data as feedback.
U.S. Pat. No. 5,713,438 entitled "Method and Apparatus for Non-Model Based Decentralized Adaptive Feedforward Active Vibration Control", issued to Dino J. Rossetti et al., discloses a system for implementing a non-model based decentralized feedforward adaptive algorithm for active vibration control of an actively-driven element. The element includes preferably an inertial tuning mass and a voice coil assembly and is contained in an active vibration control system. This reference does not disclose using a model-following system.
All of these U.S. patents are hereby incorporated by reference in their entirety herein.
The present state of the art does not provide adequate path stabilization for a vehicle. The instant invention provides a solution to this problem by using acceleration feedback data and input command signals to reduce the effects of destabilizing forces on a vehicle.